Though rainwater harvesting structures were deemed mandatory in residences, government buildings and commercial structures in 2003, most of these units are non-functional – either due to structural inefficiency or lack of maintenance.
It’s that time of the year when the oft-forgotten rainwater harvesting (RWH) structure in your building should get a maintenance check – to ensure it is ready to store the rain water during the monsoon season.
Though the Tamil Nadu government made it mandatory for all buildings to build a rainwater harvesting unit in 2003, lack of expertise during installation of these structures and absence of continuous maintenance have defeated its purpose. “The question of maintenance arises if the structures are properly installed, which is not the case. More than 60 per cent of buildings don’t have an effective rainwater harvesting structure. In most houses, recharge pits (a hole of 20-feet or less) are made and PVC pipes inserted, which is ineffective. When it was made mandatory 15 years ago, there was no clear understanding of the subject,” said Sekhar Raghavan, Director, Rain Centre, Chennai.
According to Sekhar, an efficient RWH structure has a recharge well with a diameter of 2.5 feet and a depth of 15 feet, which can be cleaned annually (unlike the recharge pits). “These wells should be empty without any gravel to ensure rainwater collection,” he added.
Indukanth S Ragade, an expert on rainwater harvesting, said that rainwater is harvested from the terraces/ rooftops. “The most efficient structure is to direct the terrace water into a traditional dug well. If the terrace is kept clean, the water quality will be okay, and the structure will require maintenance annually. If a structure is inefficient, it becomes defunct. There is also a method to direct the rainwater from terraces to the borewell but that is not safe, due to mud presence in this water,” he said.
He also pointed out that recharge pits are inconvenient, especially if the intensity of rainfall is high and the pit will tend to overflow.
While rainwater from rooftops is being harvested, the water from the driveway is still being let out into the street. “The rainwater should be intercepted near the gates and channelled to similar recharge wells. Ninety per cent of driveway runoffs are not harvested. The driveway water should be harvested near the gate, through a gutter covered with perforated lid. The water will fall into the gutter and then reach the recharge well,” said Sekhar.
Currently, despite the installation of rainwater harvesting structures, the storm water drains on the streets channel the runoff into the sea. “This system has to be re-examined,” said weather blogger K Srikanth. “Chennai gets 140 cm of rainfall annually, out of which 85 cm is during north-east monsoon. The storm water drains should be linked to nearby temple tanks and waterbodies, instead of carrying the runoff to the sea. This will not only increase the level of the waterbody but also improve the water table in that locality. There is a huge potential in rainwater harvesting,” added Srikanth, who blogs at Chennaiyil Oru Mazhai Kaalam (COMK).
Experts like Sekhar concur on the critical need to reconsider the city’s water management strategies. “When it comes to RWH, the government should show the way. Instead, most RWH structures in government buildings are just recharge pits dug several years ago and not been maintained. In addition, storm water drains dump every drop of rain water to the sea. We need to divert it to waterbodies,” he added.
The Greater Chennai Corporation too is planning to implement this in the future. “In addition to the restoration of 15 temple tanks, the storm water drains will be connected to these structures,” said a senior Corporation official.
Every drop of water is critical, said the experts. “Every drop of water is precious. Now, people are realising the importance of rainwater harvesting. But we need every single building to pledge to save rainwater for future use – to ensure water sufficiency in the future,” said Sekhar.